Basic FadeIn not working!?

Basic FadeIn not working!?

I'm about to embark on really learning jQuery. The first step of which is to get a basic jquery function to work.
Everytime I learn something this way the first thing does not work for no apparent reason. It's probably something obvious but I can't move on without getting this to work.

I added jquery to the page I have two things a div called #content-container and an image with class .logo

img.logo {
   position: absolute;
   top: 10px;
   left:5px;
   height: 57px;
   width: 108px;
   border: none;
   z-index: 50;
   visibility: hidden;
   }

#content-container {
   margin: 0;
   padding: 0;
   border: none;
   width: auto;
   overflow: hidden;
   height: 450px;
   visibility: hidden;
   }


then i put this in my header...
      <script type="text/javascript">
      $(document).ready(function(){
         $("#content-container").fadeIn("slow");
         $(".logo").fadeIn("slow");
      });
      </script>


aaaaaaand... nothing.

Why? Thanks.